A conventional method for producing a fatty alcohol comprises catalytically reducing a starting material selected from among natural fats and oils, fatty acids and fatty acid esters continuously.
This catalytic reduction is performed in the presence of a hydrogenation catalyst under a pressure of from 250 to 300 bar at a temperature of 200.degree. C. or above under an excess hydrogen atmosphere.
Since a reduction of a fatty acid ester, a fatty acid triglyceride or a fatty acid is an exothermic reaction, when an alcohol is produced by catalytically reducing such fatty acid ester, fatty acid triglyceride or fatty acid with a fixed bed reactor, the reaction has been carried out under apparently isothermal conditions with liberating the heat generated during the course of the reaction in order to improve qualities of the alcohols thus produced, as disclosed in JP-A-64-47725 (corresponding to U.S. Pat. No. 5,043,485), JP-A-63-39829 (corresponding to U.S. Pat. No. 4,982,020) and JP-A-1-275542 (corresponding to U.S. Pat. No. 4,942,266) (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and U.S. Pat. No. 4,855,273 and U.S. Pat. No. 4,935,556.
When such a catalytic reduction for producing an alcohol is continuously performed with a fixed bed reactor, it is important to prolong the life of the catalyst, since the performance of the device and the productivity significantly depend on the life of the catalyst. In the conventional method wherein the temperature in a reactor is maintained under apparently isothermal conditions, the formation of by-products such as hydrocarbons and aldehydes in the alcohol product can be suppressed. When the catalytic reduction is continuously carried out in a reactor in which a catalyst is fixed (e.g., a fixed bed reactor), on the other hand, the catalytic activity lowers as the operation time is prolonged and thus it is required to elevate the reaction temperature so as to maintain the conversion ratio. However, when the reaction temperature is elevated, the formation of the by-products tends to increase.
The life of the catalyst is mainly influenced by the conversion ratio and the amounts of impurities and by-products. Thus the qualities of the alcohol product would be gradually deteriorated, even though the catalytic reduction is performed under apparently isothermal conditions. Namely, it is difficult to continuously obtain an alcohol of high qualities over a long period of time.
In the aforesaid conventional methods, the reaction is performed under approximately isothermal conditions. Therefore an alcohol of high qualities can hardly be obtained, as the deterioration of the catalyst proceeds.
Further, it is required to eliminate hydrocarbons or aldehydes formed by the excessive reaction, since the qualities of the alcohol are deteriorated by these by-products. The boiling point ranges of the hydrocarbons overlap these of short-chain alcohols and thus the starting material must be fractionated by, for example, distillation prior to the reaction. On the other hand, the aldehydes are converted into fatty alcohols of the corresponding chain length by treating with, for example, a chemical such as a reducing agent. These treatments make the procedure complicated and cause an increase in the production cost.
Therefore it has been required to develop a process for producing an alcohol by using a fixed bed reactor in which the life of the fixed bed catalyst can be prolonged and a fatty alcohol of high qualities and a high purity can be continuously produced over a long period of time.